Remove punctuation at the end of error string
Remove punctuation at the end of error string

Golint doesn't like it

[#129480773](https://www.pivotaltracker.com/story/show/129480773)

Signed-off-by: Tom Viehman <ef9e7682e71c138189ac51545830b782ff2b8b7d@pivotal.io>

mattcui/bosh-agent,gu-bin/bosh-agent,gu-bin/bosh-agent,cloudfoundry/bosh-agent,gu-bin/bosh-agent,cloudfoundry/bosh-agent,mattcui/bosh-agent,mattcui/bosh-agent